Effect of moisture on flowability of pulverized coal

Abstract

Reliable feeding of pulverized coal into the gasifier is of great importance for the pressurized entrained-flow gasification process. Moisture and corresponding interparticle force can strongly affect the flowability of pulverized coal. In this paper, flow properties of pulverized coal were measured using a PT-X powder flow tester and a FT-4 powder flow rheometer. With respect to several flow indicators including angle of repose (AOR), Hausner ratio (HR), Carr’s flowability index (CFI), basic flow energy (BFE), cohesion (C), angle of internal friction (ϕ) and flow index (ffc), pulverized coal with different moisture contents was classified into different categories and the flow properties of each category were analyzed and compared. Secondly, a combination of a continuum approach and a particle–particle approach to describe the multi-scale nature of the mechanical properties of pulverized coal were carried out. The interparticle forces of pulverized coal with different moisture contents were predicted using a microscale approach with the Rumpf equation combined with the experimental results from the shear tester. The results were further compared with those calculated using a theoretical approach with the combination of the Kelvin equation and the Laplace–Young equation. Finally, the mechanism of moisture’s effect on flow was described by the relation between the bulk structure of wet particle systems and moisture. The results indicated that moisture had different effects before and after critical values, according to which four regimes including the “dry regime”, the “dispersed moisture regime”, the “consolidated moisture regime” and the “slurry regime” were defined with increasing moisture content.